The present invention relates to communications in digital subscriber lines. More specifically, it relates to a method for reducing audible noise from a splitterless asymmetric digital subscriber line modem.
Digital Subscriber Line (xe2x80x9cDSLxe2x80x9d) is a developing modem technology that allows existing copper telephone lines to carry high bandwidth information. Familiar twisted-pair telephone lines are then able to carry high speed data communication to and from a customer site in addition to retaining a plain old telephone service (xe2x80x9cPOTSxe2x80x9d) channel for voice communication. In DSL, digital data is transmitted to the customer site directly without being converted to an intermediary analogue signal. At the customer site, a DSL modem receives the downstream digital data for a customer from a central office for a telephone company and transmits upstream digital data from the customer to the central office.
One configuration of DSL is generally termed Asymmetric Digital Subscriber Line (xe2x80x9cADSLxe2x80x9d). ADSL allows high-speed data transport to the customer site but only medium-speed data transfer from the customer site, whence the asymmetry. ADSL also allows the simultaneous use of the ADSL modem and POTS on the same telephone line. In this configuration, at a point where the twisted-pair telephone line enters the customer site, the POTS channel is split off from the ADSL modem by filters. One problem with this ADSL, however, is that a technician from the telephone company has to visit the customer site and install the splitter, referred to as xe2x80x9cthe truck roll.xe2x80x9d
To overcome this problem, another configuration of ADSL forgoes the requirement of a splitter at the customer site. This configuration is generally called xe2x80x9csplitterless ADSLxe2x80x9d and also goes under the name of xe2x80x9cG.Lite.xe2x80x9d Splitterless ADSL is described in the International Telecommunications Union-Telecommunication Standardization Sector (xe2x80x9cITU-Txe2x80x9d, formerly known as the CCITT) standard identified by xe2x80x9cG.992.2xe2x80x9d which is incorporated herein by reference. ITU-T standards can be found on the World Wide Web at the Universal Resource Locator (xe2x80x9cURLxe2x80x9d) xe2x80x9cwww.itu.ch.xe2x80x9d Splitterless ADSL modems include those manufactured by 3Com Corporation of Santa Clara, Calif., Lucent Technologies of Murray Hill, N.J., Texas Instruments of Dallas, Tex., and others.
In splitterless ADSL, an ADSL modem directly shares the same twisted-pair telephone line as a POTS telephone without the intervention of a splitter. Sharing the same twisted-pair telephone line, however, may result in some of the ADSL signal bleeding over into the audible frequency range of the POTS telephone. Audible noise effects, such as a buzzing in the earpiece or speaker, are heard on the POTS telephone when off-hook. The noise effect is the response of the internal circuitry of the telephone to the ADSL signal. Moreover, each telephone has a different response to the ADSL signal: some telephones can be rather quiet, such as many of the cordless telephones, while other telephones produce a severely loud effect making the telephone itself unusable.
It is desirable, therefore, to reduce the audible noise in the telephone from the ADSL modem without the introduction of a splitter. It is also desirable to achieve noise reduction for a wide range of telephone models. This may allow customers to use their telephones while the ADSL modem is transferring data.
In accordance with preferred embodiments of the present invention, some of the problems associated with audible noise in a POTS telephone from a splitterless ADSL modem are overcome. A method for reducing noise from an ADSL modem is provided. One aspect of the invention includes a method for reducing audible noise in a telephone from a splitterless Asymmetric Digital Subscriber Line modem, where the telephone and the modem share a telephone loop, to enable simultaneous use of the telephone and the modem. The method includes measuring a first spectral characteristic for the telephone loop when the telephone is on-hook. The first spectral characteristic is measured by the modem. The method further includes measuring a second spectral characteristic for the telephone loop when the telephone is off-hook. The second spectral characteristic is measured by the modem. A power cutback value is calculated for the modem. The power cutback value is determined from the first spectral characteristic and the second spectral characteristic. Transmitted power from the modem is limited by an amount equal to the power cutback value.
For example, the method and system of the present invention may provide for reduction of audible noise in the telephone from a G.Lite modem. The present method and system may achieve the noise reduction for a wide range of telephone models. The method and system described herein may allow customers to use their telephones while the G.Lite modem is transferring data.